Ion implantation is a typical technique for fabricating semiconductor devices. Ion implantation may be used to change the electronic properties of semiconductor devices by adding specific impurities (i.e., dopants) to the target regions of semiconductor substrates. To be specific, in conventional ion implantation, a desired ion species to be implanted into the wafer may be ionized by electrons emitted by an electrode, accelerated to a predetermined kinetic energy, and directed as an ion beam towards the surface of the semiconductor substrate loaded in an ion implantation chamber. Because of the kinetic energy of ions, the desired ion species may penetrate into the semiconductor substrate to a certain depth. As such, the desired ions may be embedded (i.e., implanted) into the semiconductor substrate, which may thereby change the electrical properties of the semiconductor devices. However, conventional ion implantation techniques have not been entirely satisfactory in all respects.